Thalamic Contributions to Internal Models for Motor Control
by Shirin Mahdavi
Date of Examination:2024-06-18
Date of issue:2025-02-24
Advisor:Prof. Dr. Melanie Wilke
Referee:Prof. Dr. Melanie Wilke
Referee:Prof. Dr. Alexander Gail
Persistent Address:
http://dx.doi.org/10.53846/goediss-11092
Files in this item
Name:ShM_PhD_thesis.pdf
Size:9.42Mb
Format:PDF
Description:Thesis
The following license files are associated with this item:
Abstract
English
The ability of the motor system to control movements ensures successful goal-directed actions through our interaction with the environment. Motor adaptation is a process through which we maintain and adapt the existing well-learned actions in response to changes in the environment and the body. It has been suggested that this process engages brain networks of cortical and subcortical structures, including the thalamus. Although there has been great interest in how motor adaptation is encoded in the brain over the past decades, the underlying neural mechanisms remain poorly understood. In particular, the thalamus, with its extensive connections to the cerebello-cortical network, has received less attention, and studies focusing on the thalamus are scarce. Our goal was to enhance our understanding of the thalamus’s contribution to motor learning in humans. To achieve this, we employed a visuomotor adaptation paradigm combined with functional magnetic resonance imaging in healthy participants and used a similar adaptation task in a behavioral study involving a series of patients with thalamic stroke. In the first study, we aimed to identify neural correlates governing motor adaptation. Utilizing a visuomotor adaptation task in an fMRI setting, participants adapted to systematically introduced visual perturbations and continuously reported the predicted outcome of their movements (hand localization). Our findings showed that learning to adapt to small perturbations engaged a network of brain regions, including the cerebellum and fronto-parietal regions. Within the thalamus, we observed a positive correlation between the activation level of the bilateral medial dorsal nuclei and the adapted hand measured at each adaptation step. Additionally, we tested whether adaptation resulted in changes in perceived hand position. Behavioral analysis confirmed that after every step of adaptation, the perceived hand position shifted in the direction of the imposed perturbation. The neuroimaging analysis revealed that this behavioral change relied on a pathway that engaged the cerebellum, medial dorsal nuclei, and ventral lateral nuclei. A separate ROI analysis underscored the behavioral correlation with neural activity within overlapping regions of the activation map and additionally within the medial pulvinar and motor cortex. We then studied whether adaptation is disrupted as a result of damage to the thalamus. We recruited several stroke patients with thalamic lesions and tested them in a similar step-wise adaptation task while we tested other measures of adaptation (generalization and hand localization). We observed that most patients adapted in a manner similar to healthy participants. Furthermore, adaptation was accompanied by changes in reach direction to novel targets (generalization) and recalibration of efference-based predictions (hand localization). Although the lesion locations varied among the patient population, we found that patients who adapted did not have sizable lesions in motor thalamic nuclei, particularly ventral lateral or ventral anterior nuclei. On the other hand, a patient with a lesion affecting a broader region encompassing bilateral medial dorsal nuclei, the pulvinar nucleus, and the right ventral lateral/anterior nuclei did not show a lasting adaptation effect when tested with the left hand. Although much remains to be understood about the contribution of thalamic nuclei to motor adaptation, the results demonstrated in this thesis offer a fresh perspective on the role of the thalamus in motor learning.
Keywords: Motor learning; Thalamic lesion; Visuomotor adaptation; fMRI; Thalamus; Sensory prediction error
